The present invention generally relates to an automated material handling system (AMHS) and stockers and more particularly, relates to an interbay transfer interface between an AMHS and a stocker by using open-top containers positioned on a conveyor belt for transporting wafer cassettes or other parts in-between stockers.
In the manufacturing of a semiconductor device, the device is usually processed at many work stations or processing machines. The transporting or conveying of partially finished devices, or work-in-process (WIP) parts, is an important aspect in the total manufacturing process. The conveying of semiconductor wafers is especially important in the manufacturing of integrated circuit chips due to the delicate nature of the chips. Furthermore, in fabricating an IC product, a multiplicity of fabrication steps, i.e., as many as several hundred, is usually required to complete the fabrication process. A semiconductor wafer or IC chips must be transported between various process stations in order to perform various fabrication processes.
For instance, to complete the fabrication of an IC chip, various steps of deposition, cleaning, ion implantation, etching and passivation steps must be carried out before an IC chip is packaged for shipment. Each of these fabrication steps must be performed in a different process machine, i.e. a chemical vapor deposition chamber, an ion implantation chamber, an etcher, etc. A partially processed semiconductor wafer must be conveyed between various work stations many times before the fabrication process is completed. The safe conveying and accurate tracking of such semiconductor wafers or work-in-process parts in a semiconductor fabrication facility is therefore an important aspect of the total fabrication process.
Conventionally, partially finished semiconductor wafers or WIP parts are conveyed in a fabrication plant by automatically guided vehicles or overhead transport vehicles that travel on predetermined routes or tracks. For the conveying of semiconductor wafers, the wafers are normally loaded into cassettes pods, such as SMIF (standard machine interface) or FOUP (front opening unified pod), and then picked up and placed in the automatic conveying vehicles. For identifying and locating the various semiconductor wafers or WIP parts being transported, the cassettes or pods are normally labeled with a tag positioned on the side of the cassette or pod. The tags can be read automatically by a tag reader that is mounted on the guard rails of the conveying vehicle.
In an automatic material handling system (AMHS), stockers are widely used in conjunction with automatically guided or overhead transport vehicles, either on the ground or suspended on tracks, for the storing and transporting of semiconductor wafers in SMIF pods or in wafer cassettes. For instance, three possible configurations for utilizing a stocker may be provided. In case A, a stocker is utilized for storing WIP wafers in SMIF pods and transporting them first to tool A, then to tool B, and finally to tool C for three separate processing steps to be conducted on the wafers. After the processing in tool C is completed, the SMIF pod is returned to the stocker for possible conveying to another stocker. The configuration in case A is theoretically workable but hardly ever possible in a fabrication environment since the tools or processing equipment cannot always be arranged nearby to accommodate the processing of wafers in the stocker.
In the second configuration, a stocker and a plurality of buffer stations A, B and C are used to accommodate different processes to be conducted in tool A, tool B and tool C. A SMIF pod may be first delivered to buffer station A from the stocker and waits there for processing in tool A. Buffer stations B and C are similarly utilized in connection with tools B and C. The buffer stations A, B and C therefore become holding stations for conducting processes on the wafers. This configuration provides a workable solution to the fabrication process, however, requires excessive floor space because of the additional buffer stations required. The configuration is therefore not feasible for use in a semiconductor fabrication facility.
In the third configuration, a stocker is provided for controlling the storage and conveying of WIP wafers to tools A, B and C. After a SMIF pod is delivered to one of the three tools, the SMIF pod is always returned to the stocker before it is sent to the next processing tool. This is a viable process since only one stocker is required for handling three different processing tools and that no buffer station is needed. This configuration illustrates that the frequency of use of the stocker is extremely high since the stocker itself is used as a buffer station for all three tools. The accessing of the stocker is therefore more frequent than that required in the previous two configurations.
FIG. 1 illustrates a schematic of a typical automatic material handling system 20 that utilizes a central corridor 22, a plurality of bays 24 and a multiplicity of process machines 26. A multiplicity of stockers 30 are utilized for providing input/out to bay 24, or to precessing machines 26 located on the bay 24. The central corridor 22 designed for bay lay-out is frequently used in an efficient automatic material handling system to perform lot transportation between bays. In this configuration, the stockers 30 of the automatic material handling system become the pathway for both input and output of the bay. Unfortunately, the stocker 30 frequently becomes a bottleneck for internal transportation. It has been observed that a major cause for the stockers 30 to be the bottleneck is the input/output ports of the stockers.
In modern semiconductor fabrication facilities, especially for the 200 mm or 300 mm FAB plants, automatic guided vehicles (AGV) and overhead hoist transport (OHT) are extensively used to automate the wafer transport process as much as possible. The AGE and OHT utilize the input/output ports of a stocker to load or unload wafer lots, i.e. normally stored in POUFS. FIG. 2 is a perspective view of an overhead hoist transport system 32 consisting of two vehicles 34,36 that travel on a track 38. An input port 40 and an output port 42 are provided on the stocker 30. As shown in FIG. 2, the overhead transport vehicle 36 stops at a position for unloading a FOUP 44 into the input port 40. The second overhead transport vehicle 34 waits on track 38 for input from stocker 30 until the first overhead transport vehicle 36 moves out of the way.
Similarly, the OHT system is also used to deliver a cassette pod such as a FOUP to a process machine. This is shown in FIG. 3. When an OHT system is utilized in transporting a cassette pod to a process machine, problems arise when the interfab transportation plans uses a stocker (commonly known as an xe2x80x9cAS/RS stockerxe2x80x9d) to deliver baskets, i.e., open-top containers, between fabs. It is therefore difficult to interface with an automated material handling system of the OHT inside a fab. Problems caused including the need for an operator to transfer a FOUP from a basket of an AS/RS stocker and the AMHS of the fab plant. One of the problems is ergonomics since the weight of a fully loaded FOUP is approximately 8.7 kg. Another problem is the need for reserving more fab space for buffering, which translates into more space requirements and the footprint occupied by the space.
It is therefore an object of the present invention to provide an interbay transfer interface between an automated material handling system and a stocker that does not have the drawbacks or shortcomings of the conventional interbay transfer interface.
It is another object of the present invention to provide an interbay transfer interface between an AMHS and a stocker that does not require manpower to transfer FOUP between an AS/RS stocker and a fab AMHS.
It is a further object of the present invention to provide an interbay transfer interface between an AMHS and a stocker that is capable of providing just-in-time delivery without the need of waiting for an operator.
It is another further object of the present invention to provide an interbay transfer interface between an AMHS and a stocker by using existing AMHS and related SEMI(trademark) standard function for delivery.
It is still another object of the present invention to provide an interbay transfer interface between an AMHS and a stocker wherein materials between two or more fab plants may be transferred.
It is yet another object of the present invention to provide an interbay transfer interface between an AMHS and a stocker wherein sensors are utilized to detect the presence or absence of materials in an open-top container.
In accordance with the present invention, an interbay transfer interface between an automated material handling system and a stocker and a method for operating the interbay transfer interface are provided.
In a preferred embodiment, an interbay transfer interface between an automated material handling system (AMHS) and a stocker can be provided which includes a conveyor belt that is positioned juxtaposed to input/output ports of a first and a second stocker capable of moving an object therein between; a plurality of containers positioned on and carried by the conveyor belt, each of the plurality of containers further comprises an open-top for receiving the object from the AMHS therein; an aperture in each of the two opposing sidewalls forming a light passageway perpendicular to the conveyor belt, the aperture is formed in the sidewall at a height less than xc2xd of the height of the container; and at least two apertures in a bottom wall of the container for penetrating by at least two locating pins on the conveyor belt; at least two locating pins situated on the conveyor belt for engaging the at least two apertures in the bottom wall of the container, the locating pins further comprises sensors for sensing the presence of a container placed on top; a wave emitting/receiving device positioned juxtaposed to the conveyor belt for sending a wave through the apertures in the opposing sidewalls of the container for sensing the presence or absence of an object in the container; a controller for receiving signals from the wave emitting/receiving device and the sensors on the locating pins and for indicating a full/empty status of the container.
The interbay transfer interface between an AMHS and a stocker may further include a plurality of plates situated spaced-apart on the conveyor belt, each of the plurality of plates further includes at least two locating pins on a top surface of the plate for receiving the at least two apertures in the bottom wall of the container. Each of the bottom wall of the container may further include an indented area in a top planar surface for receiving a wafer cassette. The first stocker and the second stocker may be situated at least 10 m apart. The sensors on the at least two locating pins may be contact sensors, or may be weight sensor. The wave emitting/receiving device may be an optical wave emitting/receiving device, or a sound wave emitting/receiving device. The wave emitting/receiving device may be an infrared light emitting/receiving device. Each of the plurality of containers may further include a removable cover for sealing the open-top from dust.
The present invention is further directed to a method for the interbay transfer of an object between an AMHS and a stocker by the operating steps of first positioning a conveyor belt juxtaposed to input/output ports of a first and a second stocker capable of moving an object therein between; positioning and carrying a plurality of containers on and by the conveyor belt, each of the plurality of containers further includes an open-top for receiving the object from the AMHS therein; an aperture in each of two opposing sidewalls forming a light passageway perpendicular to the conveyor belt, the aperture being formed in the sidewall at a height less than xc2xd of the height of the container; and at least two apertures in a bottom wall of the container for penetrating by at least two locating pins on the conveyor belt; providing at least two locating pins on the conveyor belt and engaging the at least two apertures in the bottom wall of the container, the locating pins further includes sensors for sensing the presence of a container placed on top; sending a wave by a wave emitting/receiving device positioned juxtaposed to the conveyor belt through the apertures in the opposing sidewalls of the container and sensing the presence or absence of an object in the container; sending signals to a controller from the wave emitting/receiving device and the sensors on the locating pins indicating a full/empty status of the container; and conveying the object in the container from the first stocker to the second stocker.
The method for the interbay transfer of an object between an AMHS and a stocker may further include the step of covering the open-top of the container with a dust-proof cover. The method may further include the step of sending an infrared light by an infrared emitting/receiving device through the apertures in the opposing sidewalls of the container, or sending an ultrasonic wave by an ultrasonic wave emitting/receiving device through the apertures in the opposing sidewalls of the container. The method may further include the step of mounting a plurality of plates spaced-apart on the conveyor belt, each of the plurality of plates includes at least two locating pins for receiving the at least two apertures in the bottom wall of the container. The method may further include the step of providing an indented area in a top surface of the bottom wall of the container; and positioning a wafer cassette in the indented area.